The present invention comprises a disposable diaper having elasticized leg and/or waist encircling areas, and a method and apparatus for manufacture of the diapers. The elastic areas are provided by a heat shrinkable elastomeric material of the type that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form.
Garments having localized elasticized areas for ensuring relatively tight fits around such body zones as wrists, waist or thighs have long been manufactured. Initially, and still to a certain extent, the elastic has been applied by sewing while held in a stretched condition. When relaxed, the elastic causes a shirring or puckering of the elasticized area of the garment. Sewing elastic is a relatively slow and expensive manufacturing operation. Many inventors have dedicated their energy to findidng simpler methods of attaching elastic. As one example, Gray, U.S. Pat. No. 1,544,312, used a partially cured rubber strip which was mechanically crimped to the garment and later heat cured. Maxey, U.S. Pat. No. 2,905,181, used a band of nitrile rubber which was heat sealed to a moisture impervious polyvinyl chloride film.
Disposable diapers for infants have been the subject of a great deal of inventive activity to prevent leakage. One very successful effort in this regard was the use of a box pleat around the thigh areas of an infant. A diaper of this type is described by Duncan et al in U.S. Pat. No. Reissue 26,152. While this construction represented a major step forward, it still did not provide an entirely satisfactory solution to the problem of leakage. Another, more toward an ultimate solution is described by Buell in U.S. Pat. No. 3,860,003. The Buell diaper used narrow ribbons of stretched elastic along each longitudinal side margin in the thigh encircling areas. This construction has been so highly successful that it has been emulated and improved upon by subsequent inventors in the field. The following U.S. Patents are exemplary of these later developments: Woon et al, U.S. Pat. Nos. 4,050,462; Strickland et al, 4,253,461; Sigl et al, 4,437,860; and Teed, 4,405,397. The Strickland et al product represents a move beyond diapers suitable only for infants and is a product principally adapted for use by incontinent adults. Schaar, in U.S. Pat. No. 4,951,150, shows an infant diaper having an elasticized waist encircling area designed for reducing leakage from that portion of the product.
The above list is presented primarily to indicate historical development of diapers having elasticized zones and is not intended to be fully inclusive of all such products which have been developed. All of these examples use an elastic material which is normally a relatively narrow ribbon of natural rubber adhesively bonded between the backsheet and cover sheet of the diaper. The use of adhesive bonding, usually with flexible hot melt adhesives, has enabled the production of elasticized disposable diapers at high rates of speed.
During the later part of the time period represented by the above patents, a parallel approach has been developing using non-rubber elastomeric materials. These are based on a wide variety of synthetic polymers which typically are uniaxially or biaxially stretched during their manufacture into relatively thin film. This stretching induces stresses which are frozen into the product when it is cooled while being held under uniaxially or biaxially applied tension. Certain of these materials retain a memory of their dimensions in the original unstretched state. Depending on the particular polymer chosen, and its method of manufacture, by heating to a specific predetermined temperature, the material will shrink back to approximately this original dimension. These polymeric products can be readily tailored to be of elastomeric nature. The term "elastomeric" is interpreted in various ways, but here it is generally meant to mean that a product may be stretched to at least about 120-140% of its original length and return to that length without permanent deformation when the stretching force is released. Many of the products available are relatively inelastic in their uni- or biaxially oriented heat unstable forms and would not meet the above criterion. However, these become fully elastic when heat shrunk. A further feature of many of these polymers is that they can be heat sealed or bonded to other materials at a temperature below the point which will cause heat shrinkage. This is especially convenient for the manufacture of elasticized garments since it infers that the material may be applied without the need to be held under tension. A subsequent heating step is all that is needed to produce an elasticized zone.
While many polymeric materials of generically different types can be cited as being useful in the above application, the following U.S. patents should be considered as being exemplary: Perrin et al U.S. Pat. Nos. 2,200,249; White, 2,953,551; Cook et al, 3,086,242; Holden et al, 3,265,765; and Pellicciari et al, 3,551,540. The following British patents also disclose useful polymer compositions: Nos. 866,816; 866,820; 866,821; 866,822; and 1,010,064.
The original application of heat shrunk elastic to garments appears to have been done by Mason as shown in U.S. Pat. No. 3,245,407. Here the inventor produced plastic panties with heat shrunk elasticized leg and waist zones. Mason showed other applications as well. Later, Althouse in U.S. Pat. No. 3,639,917 showed the use of heat shrinkable elastic ribbons in other applications such as wrist, cuffs on disposable hospital garments. Massengale et al, in U.S. Pat. No. 3,819,401, and Koch et al, in U.S. Pat. No. 3,912,565 show the use of specific heat shrinkable materials for making elasticized areas in garments such as panties. Schirmer, in U.S. Pat. No. 3,755,062, shows the use of a film of heat shrinkable materials for making bulked fabric articles such as nonwoven rugs.
Natural rubber is a relatively expensive product and for this and other reasons, it is normally used in the form of threads or relatively narrow ribbons when used to elasticize portions of garments. A disadvantage of this construction is that the elasticized portion of the garment frequently presents a small and very narrow bearing area against the skin of the wearer. Thus, if the purpose of the elasticized area is to prevent leakage, as in the case of an elastic leg diaper, the elastic must be held under relative high tension to provide a tight seal. This will frequently result in chafing and general discomfort to the wearer. One solution to this problem has been to use parallel narrow strips of rubber elastic to increase the bearing area. A diaper having this type of construction is seen in Repke, U.S. Pat. No. 4,430,086. While this approach has been effective, it is relatively expensive because of the additional elastic required. It also considerably complicates manufacture of the product. For this reason, disposable diaper designers have turned to the use of heat shrunk elastomers which can be used in the form of relatively wider ribbons to increase bearing area.
Heat shrinkable materials became of interest to diaper designers as another method for overcoming the cutting and chafing problem caused by narrow elastic. A considerable number of patents have issued, beginning about 1980, directed to the use of heat shrinkable elastic ribbons placed in marginal areas of disposable diapers. In some of those the heat shrinkable elastomer is used only in the leg areas, along the longitudinal margins. In others it is used only in the waist area along the transverse margins of the diaper. In still other constructions, the heat shrinkable elastic is used in both locations. Representative examples of disposable diapers using heat shrunk elastic are found among the following U.S. Pat. Nos.: Repke et al, 4,205,679 and 4,430,086; Mesek et al, 4,324,245 and 4,352,355; Pieniak, 4,333,782; Pieniak et al, 4,337,771 and 4,413,623; Sciaraffa et al, 4,381,781; Sigl, 4,486,192; Kievit et al, 4,515,595; and Reiter, 4,563,185. The following British patent applications are also of interest: Lash, GB No. 2,136,677A and Chapman et al, GB No. 2,136,678A.
All of the above patents use discrete ribbons of the heat shrinkable elastic materials. These differ greatly in configuration, location, method of attachment, and area in which they are heat shrunk.
The inventors of the above diapers have not discussed suitable equipment for manufacturing them at any length. In making an elastic leg diaper having rubber elastic, an end-to-end assembly is normally held under sufficient tension during manufacturing to prevent wrinkling of the edges. U.S. Pat. Nos. to Buell, 4,081,301; Gore, 4,239,578; Teed, 4,309,236, 4,325,372, and 4,405,397; Frick 4,397,704; and Frick et al, 4,371,417 are exemplary of patents showing equipment for the insertion of elastic along the longitudinal edges of disposable diapers. Sigl, U.S. Pat. No. 4,412,881 and Sabee, U.S. Pat. No. 4,227,952 show equipment for insertion of discrete lengths of tensioned elastic along longitudinal edges. In addition, these following United States patents show methods and apparatus for inserting elastic inserts transversely arcross the ends of diapers forming the waist portions: Kiela, U.S. Pat. Nos. 3,844,288; Rega, 4,240,866; Joa, 4,284,454; and Pieniak 4,488,923. Klasek, in U.S. Pat. No. 4,293,367 shows a method and apparatus for contouring elastic around longitudinal leg cutouts of disposable diapers. This list is cited as being exemplary only and is not intended to be all inclusive. None of the patents noted above are specifically concerned with the insertion of an untensioned heat shrinkable polymer ribbon and its subsequent heat treatment.